It depends whether it's a picture already on the internet or a personal one you have in local storage but in either case you need to be in the full editor(button under quick reply box).

For internet images you need to insert image tags by clicking the Ing button. You then need to insert the image's location between the middle square brackets ][

For local images click on the green word attachments below the reply box. This should bring up an add files button. If you click on this it opens the file dialogue pop-up in which you can navigate to your file's location. There is a restriction of 3 files per post and on the size of the file and image dimensions so you may need to edit the file to load it.

Most small children don't need telling: they tell me. I'm at the other end of the age spectrum and I need everything thread-to-needle, and then some. I hate to comment on other people's instructions, especially when they know more than I do, but I know from experience that adding pictures on forums can be complicated till you know how.

Resizing can be an issue. If the file size is OK when you try to add it you will get a green tick on the right hand side. If you get that tick you have managed it and then it's just a matter of where you want your picture to appear in your post. If you click "Preview" it will show you where it intends putting it. If you want it in a particular position, put the cursor where you want it and click "Place inline" then have another preview to check.

If you get a red "X" rather than a tick, you need to re-size. I find MS Paint the easiest way to do it. (Paint is still there in Windows 10) Open your image in Paint, then choose the resize option. I can never remember the maximum permitted size so I just reduce the pixels by trial and error.

I've been there before and got very frustrated so if anything needs more clarification - so long as it's simple enough for an old simpleton - please ask.